Spark plug tester



July 27, 1954 E W, PlERCE Eq: AL 2,685,060

SPARK PLUG TESTER Filed July l5, 1949 3 Sheets-Sheet l Bnvcntors 50?/ n? ci July 27, 1954 E. w. PIERCE ETAL 2,685,060

SPARK PLUG TESTER Filed July 15, 1949 5 Sheets-She??l 2 July 27, i954 v E. W. PIERCE A1:1- AL 2,685,060

SPARK PLUG TESTER Filed July l5, 1949 3 Sheets-Sheet 3 a/ @L92 5 E, @ay/wond C )Hy/.pak

Patented July 27, 1954 SPARK PLUG TESTER Earl W. Pierce, Flint, Mich., and Raymond C.

Wampole, Shorewood, Wis., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 13, 1949, Serial No. 104,566

18 Claims.

This invention relates to a machine for testing electric insulation, and more particularly for testing the insulation of spark plugs.

This testing machine tests the insulation of a spark plug by quenching or insulating the spark gap with oil and applying a high voltage electric potential to the spark plug terminal. If the spark from the terminal to the shell of the spark plug is around the insulator and thus visible, the insulator is good, and if the spark is through the insulator and thus only partly visible or invisible, the insulator is defective.

The tester consists of a small press with a C frame and a vertically movable spindle or ram, such as an arbor press. The vertical ram engages the spark plug, and has an electrical contact held in contact with the spark plug terminal by a light spring. The spark plug is seated in the bore of a piston mounted in an oil cylinder. Inlet and outlet check valves in the piston maintain the oil level adjacent the top of the bore of the piston and relieve high pressure in this bore. The ram applies pressure to the spark plug to move the spark plug and piston downward in the oil cylinder to force oil around the spark plug gap. Since the inlet check valve in the piston maintains the oil level adjacent the spark plug in the bore, a minimum of piston movement is necessary to raise the oil to quench the gap. The outlet check valve controls the pressure so that the oil covers the smallest possible portion of the tip of the insulator, so that a maximum amount of the tip of the insulator may be tested.

The object of this invention is to provide a high speed spark plug testing machine whereby a minimum of movement of the spark plug and a valved piston will force the oil from a sump to quench or insulate the spark plug gap.

Another object of this invention is to provide in a spark plug testing machine in which the spark plug is mounted on a movable piston mounted in an oil cylinder to quench or insulate the spark gap, a plurality of valves to maintain the oil level adjacent the spark plug to reduce the necessary movement of the piston and a relief valve to control the pressure so that the oil covers just enough of the insulator to quench the gap.

In the drawings,

Figure 1 shows a partial elevation of the spark plug tester.

Figure 2 is an enlargement of a portion of the tester with parts in section showing the press head, the ram and oil tank.

Figure 3 is a further enlargement of the tester with parts in section showing the details of the ram and piston.

The spark plug testing machine shown in the to prevent rotation of the ram. The ram I6 isV connected to a piston rod 20 and a piston (not shown) within the fluid motor 22. The conduits 24 and 26 supply suitable fluid pressure to raise and lower the piston and ram assembly. The base of the iluid motor 22 is attached to plate 28 mounted on top of the head I4. Downwardly extending members integral with or suitably attached as by welding to the plate 28 are anchored to the head I4 by bosses 32 and bolt 34, in order to secure the iluid motor 22 on the frame head.

The ram head 3B consists of a central cylindrical portion 38, an upper cap and a lower cap 42. The ram head 36 is secured to the ram I6 by means of a two-part collar having one part 44 secured to the upper cap 40 and a second part i5 secured by screws or bolts to the Iirst part to clamp about the end of the ram I6. The central cylindrical portion 38 of the ram head has a central internally threaded portion 48 of reduced diameter to receive a threaded plug 50 of insulating material. On opposite sides of the cylindrical portion windows 45 are located above the internally threaded portion 48 and plug 50 to provide access for the electrical conductor member 62. Below the plug 5D the cylindrical portion and lower cap 42 have suitable windows 4l on opposite sides to view the spark plug 'II being tested. With the aid of the mirror 49 both sides of the spark plug may be viewed at once.

The plug 50 has a central bore 52 to provide a guide for the reciprocally mounted contact rod 54. A spring 56 is positioned around the rod 54, and seats at one end against the plug 50 in a counterbore surrounding the rod and at the other end against a stop or abutment 58 iixed to the rod. The spring exerts a light pressure on the rod 54 to hold it in contact with the electrical ter.-

- minal of the spark plug with suiicient force to maintain electrical contact. At the upper end of the rod 54 suitable nuts 60 are provided to secure an electrical conductor 62 to the rod and to provide an abutment to retain the rod 54 and spring 56 in position when the ram is up. These nuts also serve as an adjustment for the rod 5% for various length plugs. This conductor 62 is .connected to one terminal of a suitable source of high voltage electricity while the machine is grounded to the other terminal.

The lower cap l2 which is secured to the cyline drical portion 33 of the ram head has a central threaded aperture 6d to interchangeably receive various pressure plates 55 having different sized central apertures E8 for each of the different sized spark plugs that are to be tested in the machine. Each of the pressure plates ffi has a central shouldered aperture E8 which engages the shell o" the spark plug 'il to hold the spark plug downwardly in order to quench the gap in the oil. The plates 56 also have Spanner wrench sockets to receive a spanner wrench to facilitate insertion and removal of the plate 5S.

The oil tank 'M is mounted on and suitably secured to the platen l2. The tank may have the central boss 'F6 on the outside of the base to provide simplified locating means in connection with the bore 'il in the base. The tank has a cover 18 with a large central aperture Sii engaging and positioning the opened end of cylinder 82, while a bore 8| in the inside of the base o tank 1li receives and positions the closed end of cylinder 82. Suitably located in the cover are a vent elbow Ed, a filler plug t and a sticlitype oil level gage 88. A piston Se is slidably mounted in the cylinder S'Zrand has a gasket 9:2 set in an annular peripheral recess at the lower edge of the piston. A coil spring gli seated on the closed end or bottom of the cylinder 82 engages the gasket S2 and holds it in contact with the piston and resiliently urges the piston toward the top of the cylinder'. The upper end of the piston'has a reduced portion to provide a shoulder 95 which engages a covered stop plate 98 suitably secured to the cover 'E3 by screws. The cover stop plate 98 has a central aperture |33 having a slightly smaller diameter than the internal diameter of the cylinder, so that it will engage the shoulder S5 on the piston to limit the outward movement of the piston under the influence of the spring 95. When the shoulder Q6 engages the stop plate 93 the ports |62 in the cylinder wall are uncovered to allow oil to ilow into the lower portion of the cylinder below the piston. The upper portion oi the piston @6l has a central bore |534 to receive an adapter having a central. bore i138 to receive the end of the spark plug ll. A gasket Ht is set on the top surface of the adapter les to provide a seal between the spark plug shell and the adapter. An annular clamp or securing member H2 having an inwardly extending ange which centrally locates the gasket llt and the adapter i965 and clamps the adapter to the piston, is secured to the piston by suitable screws.

The bore |63 in the adapter connects with the bore ill and axial passage H55 which is plugged at the end, and transverse passage H5 which is also plugged at the end to provide a continuous passage from the spark plug to the check valve passage i8 and through the check valve passage to the lower face of piston 91]. This series of bores and passages provides a continuous passage from the upper face to the lower faces of the piston. The check valve |253 has a suitable body with a seat and valve stern guide for the stein |22, which has a head engaging the valve seat and a stop at the other end. A compression spring |24 engages the base of the cylinder t2 to open the valve and'allow uid to flow through valve passage H8 and passages |||l and HS to bores lll and IGS to quench the gap of the spark plug 1|.

Near the top of the adapter a plurality of radial relief passages |2 are formed. These relief passages connect with an annular space be tween the adapter |66 andthe clamp H2. This annular space is connected to the bottom of the piston by a relief valve passage |28 having a valve seat |36. A ball valve |32 is resiliently urgedv in contact with the valve seat by a spring ll supported by the adjustable abutment |35. This adjustable abutment ISS is threaded into a support |33 secured in a bore in the piston and locked by a suitable lock nut. .A cap |46 threaded on the support provides protection for the adjustable abutment |35. Just below the relief valve |36 a transverse outlet passage M2 connecting passage |23 to the side oit the piston provides an outlet from the relief valve to the outside of the piston. An outlet passage IM in the cylinder allows the oil to ow to the tank.

Though this spark plug testing machine is particularly adapted for testing miniature spark plugs of less than one inch in length, the general principle may be used in testing spark plugs ofA any size. In testing spark plugs on this machine the ram head 35 is moved upward by the fluid motor 22. Then the spark plug 1| is seated on the gasket H0 of the piston s@ which is heldv in its uppermost position by the spring Srl. Then the iiuid motor moves the ram head down to engage the plug. The end of the electrical contact rod "it rst engages the terminal of the spark plug ll. As the ram head moves a short distance further the rod 5t moves and compresses the spring 56 and then the adapter t@ engages' the shell of the plug '1| and seals it to the gasket H0.

Further movement of the ram moves the piston 9@ downward. As the piston moves down the seal 92 closes the ports |92 in the cylinder and thus traps oil in the bottom of the cylinder. The pressure of the trapped oil in the bottom of the cylinder opens the valve |22 to allow oil to now up the valve passage H8, the transverse passage HE and axial passage Il@ to the bore |62 into which the base of the spark plug 'H is seated. The oil under pressure is forced into the cavity at the base of the spark plug and surrounds the plug electrodes at the gap to prevent a spark at this point. The height to which the oil rises about the insulator, which should be the minimum necessary to quench the spark gap, is controlled by the relief valve pressure setting.

It the oil pressure is too high the pressure on the spark plug is relieved by ball valve |38. The bore H33 immediately adjacent the spark plug is connected by passages 52S and |28 to the valve i. The pressure maintained on the electrodes at the gap is normally four pounds for miniature plugs. However, if more or less fluid pressure is needed to force the oil around the electrodes at the gap the adjusting screw abutment |35 may be moved to vary the spring pressure on the ball |32 and thus vary the pressure.

When the gap between the electrodes of the spark plug li is quenched by the eil the high potential electricity applied through the rod 5c will jump from the spark plug terminal through the air gap to the spark plug shell if the insulator is in good condition. However, if the insulator is defective the high potential electricity will pass from the center electrode through the insulation to. the shell without producing the large visible arc over the entire surface of the insulator. Thus the good insulators are indicated by the visible spark or arc over the insulator.

In order to remove the spark plug the ram and head are moved upward by the fluid motor 22. The piston Si] is moved up with the head by the spring 94. During the upward movement the valve |20 is held open due to the fact that the stem |22 remains in contact with the bottom of the cylinder B2. Thus the oil pressure on the bottom of -spark plug 'II is relieved and the oil is allowed to recede slightly below the base of the spark plug in bore |08, after an upward movement suiicient to relieve this pressure and lower the oil level, the valve I2!! closes to keep the uid passages IIli, H6 and IIB and the bores |04 and |08 substantially lled with oil. Since the oil is held in these passages the proper oil pressure can be applied at the base on the spark plug 'il with a very small movement of the piston.

Substantially at the same time or with a very slight further upward movement of the piston the ports |02 in the cylinder 82 open to enable the oil in the tank 'M to fill the space beneath the piston by gravity. At this point the upward movement of the piston 9i) is stopped when the Shoulder 95 engages the top stop plate 98. With further upward movement the ram head 36 releases the spark plug |I and enables the operator to place another spark plug in the machine.

The above described embodiment is illustrative of the invention. It will be seen that various modifications of the invention may be made within the terms of the claimed invention.

We claim:

1. In a spark plug tester, a cylinder closed at the bottom end, a piston in said cylinder slidable between top and bottom stops, a bore in said piston extending from the top end to the bottom end, resilient means urging said piston against said top stop, means filling the bottom portion of said cylinder with fluid when the piston is moved against the top stop by said resilient means, a one-way valve in said bore preventing return of fluid to the bottom portion of said cylinder.

2. In a spark plug tester, a cylinder closed at the bottom end, a piston in said cylinder slidable between top and bottom stops, a bore in said piston extending from the top end to the bottoni end, resilient means urging said piston against said top stop, means filling the bottom portion of said cylinder with fluid when the piston is moved against the top stop by said resilient means, a one-way valve in said bore preventing' return of iluid to the bottom portion of said cylinder, and means to hold said one-way valve open when the piston is in the lower position.

3. In a spark plug tester, a cylinder closed at the bottom end, a piston in said cylinder slidable between top and bottom stops, a bore in said piston extending from the top end to the bottom end, resilient means urging said piston against said top stop, means lling the bottom portion of said cylinder below said piston with fluid when the piston is moved against the top stop by said resilient means, a one-way valve in said bore preventing return of fluid to the bottom portion of said cylinder, means to hold said one-way valve open when the piston is near the lower position and a relief valve connected to said bore.

4. In a spark plug tester, a press having a guide portion and a platen portion, a ram in said guide portion, a head on said ram, said head having an apertured plate adapted to t over a spark plug having a terminal and a shell below the terminal and engage the shell, an electrical contact slidably mounted on said head, a spring resiliently holding said contact to engage the spark plug terminal, an oil tank on said platen, a cylinder closed at one end and having a top stop and being positioned in said oil tank, a piston in said cylinder slidable between the top stop and bottom, a port in said cylinder which is uncovered when the piston engages the top stop, a bore through said piston, a spark plug seat at the top end or" said bore, a one-way valve in said bore to prevent return of fluid to said cylinder.

5. In a spark plug tester, a press having a guide portion and a platen portion, a ram in said guide portion, a head on said ram, said head having an apertured plate adapted to t over a spark plug having a terminal and a shell below the terminal and engage the shell, an electrical contact slidably mounted on said head, a spring resiliently holding said contact to engage the spark plug terminal, an oil tank on said platen, a cylinder closed at one end and having a top stop and being positioned in said oil tank, a piston in said cylinder slidable between the top stop and bottom, a port in said cylinder which is uncovered when the piston engages the top stop, a bore through said piston, a spark plug seat at the top end of said bore, a one-way valve in said bore to prevent return of fluid to said cylinder, and means holding said one-way valve open when the piston is below the port.

6, In a spark plug tester, a press having a guide portion and a platen portion, a ram in said guide portion, a head on said ram, said head having an apertured plate adapted to t over a spark plug having a terminal and a shell below the terminal and engage the shell, an electrical contact slidably mounted on said head, a spring resilientn ly holding said contact to engage the spark plug terminal, an oil tank on said platen, a cylinder closed at one end and having a top stop and being positioned in said oil tank, a piston in said cylinder slidable in substantial alignment with said ram between the top stop and bottom, resilient means holding said pistons against the top stop, a port in said cylinder which is uncovered when the piston engages the top stop, a bore through said piston, a spark plug seat at the top end of said bore, said ram positioned to move the sp-ark plug and said piston, a one-way valve in said bore to prevent return of fluid to said cylinder, and means holding said oneway valve open when the piston is below the port and means to relieve excess pressure in said bore.

7. In a tester, a tank providing a iiuid reservoir having an opening at the top, a cylinder having an opening at the top end and a closed bottom end, said cylinder being positioned in said tank below said tank opening, a piston in said cylinder slidable between upper and lower positions, resilient means holding said piston at the upper limit, means communicating with said tank and said cylinder to maintain fluid in said cylinder below said piston, a bore through said piston, a, one-way valve in said bore, a spark plug seat at the top end of said bore, and means to depress said piston.

8. In a tester, a tank providing a fluid reservoir having an opening at the top, a cylinder having an opening at the top and a closed bottom end, said cylinder being positioned in said tank and being accessible through the opening in said tank, a piston in said cylinder slidable between upper and lower positions, resilient means holding said piston in the upper position, a passage in said cylinder Wall at the lower edge of the piston connecting said tank and said cylinder, a bore completely through said piston having a spark plug seat at the top and a one-way valve therein, a relief passage in said piston connecting the bore to the wall of the cylinder, a pressure relief valve` in said passage, a relief port in said cylinder connecting with said passage in all positions of said cylinder, and means to. depress said piston.

9. In a spark plug tester, a press having a guide portion and a platen portion, a ram slidably mounted in said guide portion, a head on said ram, said head having an apertured plate adapted to fit over a spark plug and engage the shell, an electrical contact slidably mounted on said head, a spring resiliently holding said contact to engage the spark plug terminal, a fluid tank on said platen, a cylinder closed at one end mounted in said fluid tank, a piston in said cylinder, means to supp-ly fluid to the space in said cylinder between the piston and the closed end of said cylinder, a bore through said piston, a spark plug seat at one end of said bore, and valve means in said bore to hold fluid in said bore.

li). In a spark plug tester, a press having a guide portion and a platen portion, a ram slidably mounted in said guide portion, a head on said ram, said head having an apertured plate adapted to fit over a spark plug and engage the shell, an electrical contact slidably mounted on said head, a spring resiliently holding said contact to engage the spark plug terminal, a fluid tank on said plateny a cylinder closed at one end mounted in said fluid tank, a piston in said cylinder, means to supply fiuid to the space in said cylinder between the piston and the closed end of said cylinder, a bore through said piston extendlng from the closed end to the open end of the cylinder, a spark plug seat at one end of said bore, a one-way valve in said bore preventing return ofV fluid to said closed end of said cylinder.

l1. In an apparatus of the character disclosed, a cylinder having an opened end, a piston movably mounted in said cylinder and having one face adjacent said opened end, a passage in said piston extending from said one face completely through said piston, said cylinder and piston including cooperating means actuated by relative movement of said cylinder and piston to supply fluid under pressure to said passage, and means operative in said passage to maintain the fluid level in said passage adjacent the said one face.

12. In an apparatus of the character disclosed, a cylinder having an opened end and a closed end, a piston movably mounted in said cylinder and having one face adjacent said opened end and another face adjacent said closed end, a passage in said piston extending from said one face to said another face to provide a fluid passage through said piston, said cylinder and piston including cooperating means actuated by movement of said piston to supply fluid under pressure to said passage, and a check valve in said passage to maintain the fluid level in said passage adjacent said one face.

13'. In an apparatus of the character disclosed, a cylinder having an opened end, a piston movably mounted in said cylinder having one face adjacent said opened end of said cylinder, a fluid test port in said one face, a passage in said piston extending from said port completely through said cylinder, said cylinder and piston including cooperating means to supply fluid under pressure to said passage to said port, means 8 operative in said passage tol maintain the fluid level in said passage adjacent said port, and a relief valve operatively connected to said passage to limit the pressure of the fluid in said passage.

14. In an apparatus of the character disclosed,

a cylinder having an opened end, a piston movably mounted in said cylinder having one facev adjacent said opened end of said cylinder, a fluid test port in said one face, a passage in said piston extending from said port completely through said cylinder, said cylinder and piston including cooperating means actuated by movement of said piston to supply fluid under pressure through said passage to said port, means f. and cylinder and urging said piston toward said open end, a passage extending completely through said piston having a one-way valve therein to maintain the fluid in said passage adjacent said one face, means on said piston to connect a member with said passage at said one face, means to move said piston against said resilient means and said cylinder and piston including cooperating means to supply fluid under pressure to said passage when the piston is moved against said resilient means.

16. In an apparatus of the character disclosed,

a cylinder having an opened end and a closed.

ton and cylinder and urging said piston toward-V said open end, a main passage extending completely through said piston, a relief passage in said piston and cylinder connecting said main' passage to the exterior of the piston and havsaid main passage, means to move said piston against said resilient means and said cylinder i. and piston including cooperating means to supply uid under pressure to said main passage.

17. In a tester, a press having a guide portion and a platen portion, a ram slidably mounted in said guide portion, a hollow head having one end secured on said ram, an apertured plate member at the other end of said head adapted to t over a spark plug terminal and engage the shell, a transverse support plate within said head located centrally between the ends of said hollow head, an electrical contact slidably mounted on and extending through said plate support into both ends of said hollow head, a first abutment on the end of said electrical contact extending toward the end of said hollow head secured on said ram, a second abutment on the end of said electrical contact extending toward said apertured plate member, a spring between said second abutment and said support resiliently holding said contact to engage the spark plug terminal, said rst abutment retaining said electrical' contact in said support, and a spark plug seat on said platen.

18. In a tester, a support, a member reciprocally mounted on said support and havingY a 9 10 top face, a passage in said member terminat- References Cited in the le of this patent ing in a port in said .end face, fluid supply and UNITED STATES PATENTS control means mcludlng cooperating means on said member and said support to supply fluid un- Number Name Date der pressure to said passage in response t0 move- 5 211751033 S0961' Oct. 3, 1939 ment of said member, means on said member to 21369320 Sjaundel's Feb. 20, 1945 maintain the fluid level in said passage adja- 253701945 Flelds Mal'. 6, 1945 cent said port in the top face, and a relief valve 401533 Wafll June 4, 1946 connected with said passage to limit the pres- 2,434,959 Smde Jal- 27, 1948 sure in said passage, 10 2,490,821 Leonard 1380.13, 1949 

